Consistency-dependent optical properties of lubricating grease studied by terahertz spectroscopy

The optical properties of four kinds of lubricating greases (urea, lithium, extreme pressure lithium, molybdenum disulfide lithium greases) with different NLGL (National Lubricant Grease Institute of America) numbers were investigated using terahertz time-domain spectroscopy. Greases with different NLGL grades have unique spectral features in the terahertz range. Comparison of the experimental data with predictions based on Lorentz--Lorenz theory exhibited that the refractive indices of each kind of lubricating grease were dependent on the their consistency. In addition, molybdenum disulfide (MoS₂) as a libricant additive shows strong absorption from 0.2 to 1.4 THz, leading to higher absorption of MoS₂-lithium grease than that of lithium grease.     

Anomalies in the optical properties of nanocrystalline copper oxides CuO and Cu2O near the fundamental absorption edge

A 0.1–0.15-eV displacement of the fundamental absorption edge in the optical absorption spectra of nanocrystalline oxide n-CuO (relative to the position of the fundamental absorption edge in the spectra of CuO single crystals) towards lower energies (red shift) is observed against the background of strong blurring. Nanocrystalline n-Cu₂O exhibits a displacement of the fundamental absorption edge towards higher energies (blue shift) by approximately 0.35 eV. The size of crystallites in n-CuO and n-Cu₂O ranges from 10 to 90 nm. The blue shift of the fundamental absorption edge of n-Cu₂O is typical of classical wide-gap semiconductors and can be explained by size quantization upon a change in the particle size. The anomalous red shift of the fundamental absorption edge of the strongly correlated nanocrystalline oxide n-CuO can be attributed to the highly defective structure of n-CuO, anomalies in the electronic structure of strongly correlated compounds based on 3d metals, and their tendency to electronic phase separation with the formation of metal-like inclusions.     

C60 adsorption on Cu(110) studied by optical spectroscopy

The formation of the interface between C₆₀ thin films and the Cu(110) surface has been investigated in situ using reflectance difference spectroscopy (RDS). The electronic interaction between C₆₀ molecules in the first monolayer and the substrate inhibits low‐energy intramolecular transitions, whereas the C₆₀ molecules above the first monolayer are effectively decoupled from the substrate. The morphology of C₆₀ thin films prepared at room temperature is thermally stable up to 500 K. Above this threshold, optical spectroscopy and low energy electron diffraction (LEED) indicate the formation of rather large three dimensional C₆₀ islands on a one monolayer thick wetting layer. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electronic and optical properties of ceramic Sc2O3 and Y2O3: Compton spectroscopy and first principles calculations

We present the first-ever experimental Compton profiles (CPs) of Sc₂O₃ and Y₂O₃ using 740 GBq ¹³⁷Cs Compton spectrometer. The experimental momentum densities have been compared with the theoretical CPs computed using linear combination of atomic orbitals (LCAO) within density functional theory (DFT). Further, the energy bands, density of states (DOS) and Mulliken's population (MP) data have been calculated using LCAO method with different exchange and correlation approximations. In addition, the energy bands, DOS, valence charge density (VCD), dielectric function, absorption coefficient and refractive index have also been computed using full potential linearized augmented plane wave (FP-LAPW) method with revised functional of Perdew–Becke–Ernzerhof for solids (PBEsol) and modified Becke Johnson (mBJ) approximations. Both the ab-initio calculations predict wide band gaps in Sc₂O₃ and Y₂O₃. The band gaps deduced from FP-LAPW (with mBJ) are found to be close to available experimental data. The VCD and MP data show more ionic character of Sc₂O₃ than Y₂O₃. The ceramic properties of both the sesquioxides are explained in terms of their electronic and optical properties.     

Electronic properties of free and supported metal clusters studied by photoelectron spectroscopy

The electronic properties of free and supported metal clusters are studied by photoelectron spectroscopy. Experimental as well as theoretical results clearly demonstrate a dramatic dependence of the level structure on the cluster size. By this an interesting way might be opened to modify the electronic, optical and chemical properties of surfaces.     

The adsorption of CO on Cu surfaces studied by electron energy loss spectroscopy

Electron energy loss spectroscopy (ELS) in the energy range of electronic transitions (primary energy 30 < E₀ < 50 eV, resolution ΔE ≈ 0.3 eV) has been used to study the adsorption of CO on polycrystalline surfaces and on the low index faces (100), (110), (111) of Cu at 80 K. Also LEED patterns were investigated and thermal desorption was analyzed by means of the temperature dependence of three losses near 9, 12 and 14 eV characteristic for adsorbed CO. The 12 and 14 eV losses occur on all Cu surfaces in the whole coverage range; they are interpreted in terms of intramolecular transitions of the CO. The 9 eV loss is sensitive to the crystallographic type of Cu surface and to the coverage with CO. The interpretation in terms of d(Cu) → 2π¹(CO) charge transfer transitions allows conclusions concerning the adsorption site geometry. The ELS results are consistent with information obtained from LEED. On the (100) surface CO adsorption enhances the intensity of a bulk electronic transition near 4 eV at E₀ < 50 eV. This effect is interpreted within the framework of dielectric theory for surface scattering on the basis of the Cu electron energy band scheme.     

Electronic excitation processes in rare gas clusters studied by electron energy loss spectroscopy

We present the electron energy loss spectra for Ar clusters as a function of incident electron energy and of cluster size. In spectra measured with 100 eV incident electron energy the bulk excitation peak becomes visible for a mean cluster size above 170 atoms per cluster. For 250 eV incident electron energy the bulk excitation peak is clearly observable even for a mean cluster size of 120 atoms per cluster. These experimental results are qualitatively reproduced by a simple calculation that accounts for the mean free path of electrons in Ar clusters; i.e., the penetration depth of incident electrons into the cluster.     

Electronic properties of YBa2Cu4O8 and Y2Ba4Cu7O15 as probed by NMR/NQR

Nuclear Magnetic Resonance (NMR) and Nuclear Quadrupole Resonance (NQR) allow the investigation of electronic properties at the atomic level. We will report on such studies in typical members of the Y-Ba-Cu-O family of high-temperature superconductors, namely YBa₂Cu₄O₈ and Y₂Ba₄Cu₇O₁₅. We will deal with temperature and orientational dependences of Cu and O Knight shifts and spin-lattice relaxation. Topics to be discussed are: (1) Existence of a common electronic spin-susceptibility (a single-spin fluid) in the planes and in the chains of YBa₂Cu₄O₈. (2) Evidence for the existence of a pseudo spin-gap in the anti-ferromagnetic fluctuations in YBa₂Cu₄O₈ and Y₂Ba₄Cu₇O₁₅. (3) Evidence for non-s symmetry of the pair wave function in YBa₂Cu₄O₈. (4) First NQR observation of a strong coupling of inequivalent Cu-O planes in Y₂Ba₄Cu₇O₁₅. (5) Alternative explanations of relaxation and Knight shift.     

Electronic structure and optical properties of ABP2O7 double phosphates

Luminescence and luminescence excitation under VUV radiation of ${\mathrm{ABP}}_2{\mathrm{O}}_7$ ($\mathrm{A}=\mathrm{Na}$, K, Cs; $\mathrm{B}=\mathrm{Al}$, In) double phosphates are studied. Two emission bands peaking near 330 and 420 nm are common for investigated ${\mathrm{ABP}}_2{\mathrm{O}}_7$ crystals. The band structure and partial densities of electronic states of perfect ${\mathrm{KAlP}}_2{\mathrm{O}}_7$, ${\mathrm{LiInP}}_2{\mathrm{O}}_7$ and ${\mathrm{NaTiP}}_2{\mathrm{O}}_7$ crystals are calculated by the full-potential linear-augmented-plane-wave (FLAPW) method. It is found that the structures of the conduction bands of ${\mathrm{ABP}}_2{\mathrm{O}}_7$ crystals, which have different B cations, are appreciably different. Experimental results are compared with results of calculations of the electronic structure. Assumptions concerning the origin of luminescence in double phosphates are made.     

Investigation on optical properties of ZnO nanowires by electron energy-loss spectroscopy

Electron energy-loss spectroscopy (EELS) and ab initio band structure calculations have been performed to determine the optical properties of wurtzite structured zinc oxide (ZnO) nanowires. Compared with other techniques, EELS significantly extends the energy range and is a useful technique for analysis of the dielectric properties on a microstructure level. The first-principles calculations allow deep insight into the experimental results. Furthermore, the polarization dependencies of optical properties have been discussed. Our results give some reference to the thorough understanding of optical properties of ZnO.     

Adsorption and decomposition of HNCO on Cu(111) surface studied by auger electron,electron energy loss and thermal desorption spectroscopy

No detectable adsorbed species were observed after exposure of HNCO to a clean Cu(111) surface at 300 K. The presence of adsorbed oxygen, however, exerted a dramatic influence on the adsorptive properties of this surface and caused the dissociative adsorption of HNCO with concomitant release of water. The adsorption of HNCO at 300 K produced two new strong losses at 10.4 and 13.5 eV in electron energy loss spectra, which were not observed during the adsorption of either CO or atomic N. These loses can be attributed to surface NCO on Cu(111). The surface isocyanate was stable up to 400 K. The decomposition in the adsorbed phase began with the evolution of CO₂. The desorption of nitrogen started at 700 K. Above 800 K, the formation of C₂N₂ was observed. The characteristics of the CO₂ formation and the ratios of the products sensitively depended on the amount of preadsorbed oxygen. No HNCO was desorbed as such, and neither NCO nor (NCO)₂ were detected during the desorption. From the comparison of adsorption and desorption behaviours of HNCO, N, CO and CO₂ on copper surfaces it was concluded that NCO exists as such on a Cu(111) surface at 300 K. The interaction of HNCO with oxygen covered Cu(111) surface and the reactions of surface NCO with adsorbed oxygen are discussed in detail.     

Electronic structure and magnetic properties of(Cu,N)-codoped3C-SiC studied by first-principles calculations

The electronic structures and magnetic properties of the Cu and N codoped 3C-Si C system have been investigated by the first-principles calculation.The results show that the Cu doped Si C system prefers the anti-ferromagnetic(AFM) state.Compared to the Cu doped system,the ionicities of C–Cu and C–Si in Cu and N codoped Si C are respectively enhanced and weakened.Especially,the Cu and N codoped Si C systems favor the ferromagnetic(FM) coupling.The FM interactions can be explained by virtual hopping.However,higher N concentration will weaken the ferromagnetism.In order to keep the FM interaction,the N concentration should be restricted within 9.3% according to our analysis.     

Electronic and optical properties of the H2O adsorbed the B-N-C nanotubes

We investigate the structures and properties of boron/nitrogen co-doped carbon nanotube with water molecules adsorbing. The electronic and optical properties of the systems are calculated by using the first-principles theory in detail. The results reveal that the doped nanotubes show hydrophilic behavior when the oxygen atoms are close to the nanotubes. The Mulliken charges redistribute and transfer between the doped carbon nanotubes and the water molecules. The band gaps of the nanotubes vary with the positions of H₂O. The positions and intensities of the reflectivity peaks are affected by the distributions of boron/nitrogen atoms and the positions of water molecules. The investigations are beneficial to further biological applications of co-doped nanotubes.